I've been reading a lot of articles about how different people have gone about building their DIY amps/preamps. I now know the huge difference capacitors in the signal path can make but what about resistors?

I have seen reference to Holco and caddock brand resisitors. What is special about these (presumably high quality) resistors? Are they just tighter tolerence types (ie. 1%). Will I hear the difference these resistors will make when substituted for the standard types (ie. 5% metal, 5% carbon)?

I live in Australia and as yet have not come across anything but the standard type resistors does anyone know where I can get the aformentioned brands or equivalents either here or overseas.

ding,
I don't know that the brands you mention have necessarily better tolerances or thermal stability. Mostly it has to do with '" " sound " ". Don't expect to find this stuff at big places like Digikey and such, the only people that care about this kind of crap are " " audiophiles " " and that means buying from some outfit like Welborne labs and others. Bottom line: get ready to get sucked out dry.

I'm not going to get involved in a debate on the audibility of resistors since there are many conflicting views. Some people prefer carbon, some metal film and some pay unjustified prices for esoteric devices. Personally, I don't think there is as much difference as there is with capacitors so I use standard 1% metal films (though I have tried Holcos).

The reason for replying to your posting is to give you a couple of UK suppliers, in case you can't find one locally.

Dan,
As arguably one of, if not the highest profile "audiophiles" in these parts, I'll have to weigh in as...an agnostic, of all things. I have done fairly extensive comparisons of capacitors in the past, but have not done any serious work with resistors. People whose hearing I trust seem to consistently indicate that Vishay, Holco, Caddock, et. al. sound better than garden variety resistors. Not having done the routine myself, I will not venture to say either way. However, I will go on record on caps, as I've done my homework there.
Some caps are audibly superior to others. Period.
I see no reason not to believe that the same would be true of resistors, but as to paying $10/ea. for Vishay...I dunno...there are an awful lot of resistors in your average piece of audio gear. It'd have to be a pretty noticable difference. On the other hand, I just got in a batch of MIT caps, and they ain't cheap. I choose to pay (yes, dearly...) for the sound quality. Is it a linear relationship; is a $20 cap twice as good as a $10 cap? No. It's the same as everything else in life--a case of diminishing returns. How high up the curve you want to go is up to you (and your wallet). Even as fanatical as I get sometimes, I don't look down my nose at people who don't (or can't afford to) buy the expensive parts. I've been poor before, and may be again. Right now, I can (oh, so grudgingly!) pay the price, and so I do.
Why haven't I done my 'homework' on resistors? (And by extension, why haven't I updated my studies on caps? [At this point several years out of date.]) Time. And money, to a lesser extent. It's damned time consuming to swap parts in and out of a circuit. The alternative is to build two (or more) identical circuits but with parts from different manufacturers. That's faster, listening-wise, and you can A-B to your heart's content, but then you get into questions like,"is the bias on this circuit really quite the same as on that one?"
Ugh. It's enough to turn one into a numbers critter due to the number of variables.
For the time being, I console myself by using good caps, and pretty decent resistors (Vishay/Dale--Vishay now owns Dale, but do not confuse these with the Vishay resistors mentioned above. Vishay is a large company that's bought lotsa other companies--Sprague, too, I believe, and Siliconix.). My reasoning here is that resistors are *much* more consistent in size than 'audiophile' caps. I can do a board layout for a 1/2W resistor and be fairly certain that a wide spectrum of other resistors will fit in the same space later. Unfortunately, the same is not true of caps. I have to bite the bullet and get the expensive stuff right out of the gate, as the layout will change depending on whether you use Infinicap, Hovland, MIT, or whatever.
Sources:http://www.tubesandmore.com (Hovland on sale)http://www.mouser.com (Vishay/Dale)http://www.bainbridge.net/percyaudio (Vishay, Roderstein, Caddock, others)http://www.sonicfrontiers.comhttp://www.hndme.comhttp://www.welbornelabs.com (generally higher in price than everyone else--but mentioned above by grataku, thought I'd throw in the address)
There are others, but these are a representative sample. Roderstein resistors aren't too pricey, as these things go (I think Audio Research used to use them, may still for all I know). Vishay is probably the worst. The Vishay/Dale are reasonable (actually cheaper than I can buy NTE stuff here locally). Geoff and I (and others) are in agreement--the prices aren't justified in terms of what goes into the parts (true for caps, too). But nobody is making you (or me) buy the stuff. It's a market economy. They offer at a price and you either buy or not, as suits you.
Two notes:
-Don't use Hovland resistors over 200V or so. (Kinda limits tube applications a bit.)
-Compare prices. Not that you wouldn't, but some of the suppliers kick in discounts based on quantity, others based on dollar amount. Make up a detailed list of what you might want, then run the list through the mill. Surprises sometimes fall out when supplier "A" suddenly drops 5% because you went over $150, but supplier "B" gives a 25% discount because you want 10 pieces.
But, Grey, is it *worth* the money? Really?
Sorry, Grey ain't here...he went out for a beer. Leave a message so he can ignore it when he gets back in.

One of the areas that these high priced resistors excel at are a rating called ppm. I forget what it stands for, it's not parts per million...I think, Anyway, what that rating indicates is the change in value for a given rating /watt over time. All resistors begin to change in value when current passes through them after a long period of time. Typical resistors, 1% metal film, have a ppm of 50 to 100, Vishay has something like 5 ppm or less. Caddock is only a bit higher. Both considered excellent. Some say that it's like having nothing in the signal path, like a straight wire. Vishay are something like $10.95 for a typical value here in the States. Caddock are about $4.00 for the same value, and are just about as good, at least that's what Micheal Percy says, a seller of DIY parts in CA. I have not ventured to buy these parts..yet.

I always wanted to build a simple circuit like the Zen with high end resistor and normal 1% to see if I could here a difference. Oh, and the tolarences for these are better than 1% too.

BTW- There is a Vishay facility about 4 miles from where I live. I once called for some samples; they didn't send any. I guess they only like to deal with areospace co's and the military. Elitist snobs!

It's called temperature coefficient, and really good
resistors (metal film and wire wound) will have lower values over both short and long term. Another figure of
merit is low noise, but generally metal film and wire wounds are the lowest anyway. Anything under 50 ppm seems to cost a good bit more. Better quality parts seem to be
of more robust physical construction too, especially for
wire wound types.

So-called tantalum resistors seem to be regarded as the very best types, but are almost impossible to find at any price. I think these are tantalum nitride, and may also be available in surface mount parts, but I'm not going to fool with that unless I absolutely can't avoid it.

Mills has a very good reputation for wire wounds, but I think any part of good physical quality and low temperature coefficient is good enough. I was going to use Mills for
emitter resistors in my Leach amplifier upgrade project, but I found good-quality substitutes locally (IRC stamped) at a lower price. I deconstructed one and found the resistive element was a relatively wide tape rather than a thin wire, which suggests a better temperature coefficient than the sand cast types I'd been using for my projects.

Lower internal inductance is a Good Thing, and possibly
non-magnetic construction throughout, but these qualities
are difficult to find in most parts and I don't worry overmuch about it.

Some types of resistors seem to be midway between metal film and wire wound, such as the bulk foil types. As I
can't afford to spend several dollars on individual resistors (other than high power wirewounds for very specific applications), I happily settle for metal film
resistors of most any sort. I think Vishay/Dale CMF55/60 types have been well-received and are available through Mouser.

As has been pointed out, some people like the sound of a good quality carbon composition resistor, but these have gone out of production and the best ones, Allen Bradley I think, are getting very rare. They don't age too well, either.

We could get into potentiometers; there's an area where I don't know of many specific good quality parts at reasonable prices.

All other things equal, a component that is not itself magnetic (magnet test) is very likely to sound better than one which is.

Electromagnetic "forces" are very much stronger when in the vicinity of magnetic (magnetizable to be simplistic -- there are 3 main types of magnetism, ferromagnetism is the "worst" one which we are identifying by this test) materials.

Bring a magnet to the store when you buy. I got this tip from Thorsten.

From memory Holco M-F resistors are a copper alloy with non-magnetic gold plated end caps, they are aged for 3 days at elevated temperatures then the values are checked, this weeds out the early failure high drift units, and justifies the premium prices (?).

As you are in Australia (I'm in Victoria) the best source I have found for quality and price is Radiospares

I seem to remeber some major change that was made to Holco metal films resistors in the last year or so that made them no longer desirable - maybe using steel in the leads now or some ferrous metal in the endcaps? Now where did I see this: Sonic Frontiers parts catalog maybe? Anybody else remember this?